1. Field
The invention relates generally to the field of telecommunications, and more particularly to systems and methods for scheduling data transmissions in a wireless communication system using scheduling requests and grants.
2. Background
Wireless communication technologies are rapidly advancing, and wireless communication systems are utilized to provide a larger and larger portion of the communications capacity that is currently available to users. This is true despite the additional technological impediments that are faced in implementing a wireless communication system, as compared to a wireline system. For instance, wireless communication systems must deal with issues relating to transmission scheduling between a base station and its mobile stations when the quality of the wireless communication channels between them is constantly changing. The base station and mobile stations must therefore deal with the issue of how much data can be transmitted in light of the prevailing conditions rather than simply scheduling transmissions, as in a wireline system.
One type of wireless communication system comprises a cellular CDMA (code division multiple access) system which is configured to support voice and data communications. This system may have multiple base stations which communicate via wireless channels with multiple mobile stations. (The base stations are also typically coupled via wireline networks to various other systems, such as a base switching station that may couple the base stations to the internet or a public switched telephone network.)
As mobile stations move through the area covered by the wireless communication system, they may communicate with multiple base stations. The mobile stations may also be handed off from one base station to another. This is referred to as a handoff between the base stations. Conventionally, because the mobile stations are handed off from one base station to another, the scheduling of transmissions, particularly transmissions from the mobile stations to the base stations, is handled by the base station controller, which is coupled to the base stations and can therefore account for the handoffs of the mobile stations.
While the transmissions are conventionally scheduled by the base station controller, this does cause some delay in the scheduling. This delay is a result of the fact that the information relevant to scheduling (e.g., a request message) is carried in Layer 3 messages that are first obtained by the base stations, and then transmitted to the base station controller, which makes appropriate scheduling decisions and then transmits the resulting scheduling information back to the base stations. Adding to this delay is the fact that Layer 3 messages have to be processed by the LAC layer (which is above the MAC layer, but below Layer 3). Also, Layer 3 messages are commonly processed by a shared CPU, rather than a dedicated CPU, although this varies from implementation to implementation. Further contributing to the delay is the propagation delay between the base station and base station controller, where Layer 3 messages are commonly processed. There is therefore a need in the art for systems and methods that perform scheduling of data transmissions without incurring the delays experienced in the prior art.